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1. Pyridinol-based CNC Pincer catalysts for carbon dioxide reduction: The big impact of one small remote group

   Papish, Elizabeth T.; Das, Sanjit; Boudreaux, Chance M.; Burks, Dalton B.; Qu, Fengrui; Rodrigues, Roberta R.; Lamb, Robert W.; Delcamp, Jared H.; Webster, Charles E. (October 2018, Southeastern Regional Meeting of the ACS)

   The first examples of a CNC pincer ligands with a central pyridinol derived ring were recently reported.  The differences in catalytic reactivity between CNC ligands with a central pyridine ring vs. a pyridinol derived ring are substantial and highly active and robust catalysts have been synthesized and studied.  In these pincer ligands, the 4-substituent can be OMe, OH, or O-, and these latter two options allow for altered catalyst properties as a function of proton concn.  Catalytic studies have used ruthenium(II), nickel(II), and other transition metals.  We have made metal complexes that can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO2 redn.  Furthermore, the methoxy group on the pyridine ring offers unique catalysis advantages not seen with the unsubstituted analog.  Our best catalysts offer selective CO formation, >300 turnover cycles, and a 40 h lifetime.  Steric and electronic ligand effects are being studied with these catalysts by exptl. and computational methods. 

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2. Can boron form coordination complexes with diffuse electrons? Evidence for linked solvated electron precursors

   https://doi.org/10.1088/2516-1075/ac495c  

   Jordan, Zachary; Khan, Shahriar N; Jackson, Benjamin A; Miliordos, Evangelos (January 2022, Electronic Structure)

   Abstract Density functional theory and ab initio multi-reference calculations are performed to examine the stability and electronic structure of boron complexes that host diffuse electrons in their periphery. Such complexes (solvated electron precursors or SEPs) have been experimentally identified and studied theoretically for several s- and d-block metals. For the first time, we demonstrate that a p-block metalloid element can form a stable SEP when appropriate ligands are chosen. We show that three ammonia and one methyl ligands can displace two of the three boron valence electrons to a peripheral 1s-type orbital. The shell model for these outer electrons is identical to previous SEP systems (1s, 1p, 1d, 2s). Further, we preformed the first examination of a molecular system consisting of two SEPs bridged by a hydrocarbon chain. The electronic structure of these dimers is very similar to that of traditional diatomic molecules forming bonding and anti-bonding σ and π orbitals. Their ground state electronic structure resembles that of two He atoms, and our results indicate that the excitation energies are nearly independent of the chain length for four carbon atoms or longer. These findings pave the way for the development of novel materials similar to expanded metals and electrides. 

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3. Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton–proton collisions at $$\sqrt{s}=13\,\text {TeV} $$

   https://doi.org/10.1140/epjc/s10052-022-10127-0  

   Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Valle, A. Escalante; Frühwirth, R.; Jeitler, M.; Krammer, N.; Lechner, L.; et al (April 2022, The European Physical Journal C)

   Abstract A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a $${\mathrm{Z}}$$ Z boson. The search uses proton–proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137 $$\,\text {fb}^{-1}$$ fb - 1 , at a center-of-mass energy $$\sqrt{s} = 13\,\text {TeV} $$ s = 13 TeV . No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits on dark photon and axion-like particle production, based on two specific models, are reported. 

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4. Pyridinol-based CNC Pincer catalysts for carbon dioxide reduction: The big impact of one small remote group

   Papish, Elizabeth T.; Das, Sanjit; Boudreaux, Chance M.; Burks, Dalton Bodine; Rodrigues, Roberta R.; Webster, Charles Edwin; Delcamp, Jared H. (April 2019, ACS National Meeting Abstracts)

   The first examples of a CNC pincer ligands with a central pyridinol derived ring were recently reported.  The differences in catalytic reactivity between CNC ligands with a central pyridine ring vs. a pyridinol derived ring are substantial and highly active and robust catalysts have been synthesized and studied.  In these pincer ligands, the 4-substituent can be OMe, OH, or O , and these latter two options allow for altered catalyst properties as a function of proton concn.  Catalytic studies have used ruthenium(II), nickel(II), and other transition metals.  We have made metal complexes that can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO redn.  Furthermore, the methoxy group on the pyridine ring offers unique catalysis advantages not seen with the unsubstituted analog.  Our best catalysts offer selective CO formation, >300 turnover cycles, and a 40 h lifetime.  Highly active self-sensitized catalysts have recently been developed.  Steric and electronic ligand effects are being studied with these catalysts by exptl. and computational methods. 

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5. Spectroscopic signatures of states in the continuum characterized by a joint experimental and theoretical study of pyrrole

   https://doi.org/10.1063/5.0123603  

   Mukherjee, Madhubani; Ragesh Kumar, T. P.; Ranković, Miloš; Nag, Pamir; Fedor, Juraj; Krylov, Anna I. (November 2022, The Journal of Chemical Physics)

   We report a combined experimental and theoretical investigation of electron–molecule interactions using pyrrole as a model system. Experimental two-dimensional electron energy loss spectra (EELS) encode information about the vibrational states of the molecule as well as the position and structure of electronic resonances. The calculations using complex-valued extensions of equation-of-motion coupled-cluster theory (based on non-Hermitian quantum mechanics) facilitate the assignment of all major EELS features. We confirm the two previously described π resonances at about 2.5 and 3.5 eV (the calculations place these two states at 2.92 and 3.53 eV vertically and 2.63 and 3.27 eV adiabatically). The calculations also predict a low-lying resonance at 0.46 eV, which has a mixed character—of a dipole-bound state and σ* type. This resonance becomes stabilized at one quanta of the NH excitation, giving rise to the sharp feature at 0.9 eV in the corresponding EELS. Calculations of Franck–Condon factors explain the observed variations in the vibrational excitation patterns. The ability of theory to describe EELS provides a concrete illustration of the utility of non-Hermitian quantum chemistry, which extends such important concepts as potential energy surfaces and molecular orbitals to states embedded in the continuum. 

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